The present disclosure generally relates to compensating focusing power in imaging optics, and specifically to use of geometric phase lenses in augmented reality (AR) head mounted displays (HMD).
An AR headset displays virtual image overlapping with image of a local area surrounding the AR headset. The virtual image is usually generated by computer. Some AR headsets use geometric phase lenses (GPLs) as focusing-optics. A GPL is an optical half-wave plate (HWP) with spatially varying optic-axis. A GPL is designed for a particular wavelength, e.g., the wavelength in a particular color band. For light having the designed wavelength, if it enters the GPL as left handed circularly polarized (LCP) light, it exits the GPL as right handed circularly polarized (RCP) light, or vice versa. There is no leakage of the light. However, for light not having the designed wavelength, circularly polarized light exits the GPL as elliptically polarized light with leakage. Thus, the focusing power of the GPLs can produce large amount of color dispersion, making an AR headset unusable, especially when used in see-through to view the local area.